Histamine is an important brain neurotransmitter and neuroregulator, and is present in all nerve cells. Histamine influences mood, appetite, sleep and thought. Histamine is a natural component of many foods, as well as the cells in the body. It is an important part of the immune and neurologic systems and is involved in the process of inflammation. Most commonly noted in Bio-Chemical testing, histamine is the most reliable marker for methylation. Note: Medications, presence of other polyamines, and allergy treatment may affect results of histamine.